Дать подробное описание объекту

(defun fact (n)
  (if (zerop n)
      1
      (* n (fact (- n 1)))))
(describe #'fact)

#<FUNCTION FACT (N) (DECLARE (SYSTEM::IN-DEFUN FACT)) (BLOCK FACT (IF # 1 #))>
is an interpreted function.

Argument list: (N)

Проследить вызовы функции

(defun fact (n) 
  (if (zerop n)
      1   
      (* n (fact (- n 1)))))
(trace fact)
(fact 3)
(untrace fact)

0: (FACT 3)
  1: (FACT 2)
    2: (FACT 1)
      3: (FACT 0)
      3: FACT returned 1
    2: FACT returned 1
  1: FACT returned 2
0: FACT returned 6
6

Итеративно инспектировать объект

(inspect #'foo)

Вызвать дебаггер в определённом месте

(break "You have entered the debugger with arguments: ~s" '(1 2 3))

You have entered the debugger with arguments: (1 2 3)

[Condition of type SIMPLE-CONDITION]

Restarts:
0: [CONTINUE] Return from BREAK loop
1: [ABORT-REQUEST] Abort handling SLIME request.
2: [ABORT] Return to SLIME top-level.
3: [ABORT] ABORT

Замерить время выполнения участка кода

(defun add-n-squares (n)
  (do ((i 0 (+ i 1))
       (sum 0 (+ sum (* i i))))
    ((> i n) sum)))

(time (add-n-squares 10000))

Evaluation took:
  0.001 seconds of real time
  0.004000 seconds of total run time (0.004000 user, 0.000000 system)
  400.00% CPU
  3,090,464 processor cycles
  212,792 bytes consed

333383335000

Посмотреть состояние памяти лиспа

(room)

Bytes permanently allocated: 90624
Bytes currently in use: 3258228
Bytes available until next GC: 180536
3258228
180536